Process for the production of a fibrid slurry



Dec. 18, 1962 P. w. MORGAN PROCESS FOR THE PRODUCTION OF A FIBRID SLURRYOriginal Filed Jan. 22, 1959 FIG. I

INVENTOR PAUL WINTHROP MORGAN ATTORNEY United States Patent vffice3,068,527 Patented Dec. 18, 1962 3,063,527 PROCESS FOR THE PRODUCTION OFA FIBRID SLURRY Paul Winthrop Morgan, West Chester, Pa., assignor to E.I. du Pont de Nemours and Company, Wilmington, DeL, a corporation ofDelaware Original application Jan. 22, 1959, Ser. No. 788,371, nowPatent No. 2,999,788, dated Sept. 12, 1961. Divided and this application.ian. 4. 1960, Ser. No. 380

6 Claims. (Cl. 18-48) This invention relates to a composition of matterand to a process for its production. More specifically it relates to amethod of producing a novel and useful nonrigid, wholly syntheticpolymeric particle as described more in detail hereinafter which isparticularly useful in the production of sheet-like structures.

bjects.It is an object of the present invention to provide a novel,non-rigid, wholly synthetic polymeric particle of matter capable offorming sheet-like structures on a paper-making machine.

Another object is to provide a method by which a novel, non-rigidparticle of a synthetic polymer, useful in the production of non-wovenstructures, can be made directly from polymer intermediates.

These and other objects will become apparent in the course of thefollowing specification and claims.

Statement of lnventi0n.The present invention provides a process for theproduction of a novel and useful non-rigid, wholly synthetic polymericparticle which process comprises shredding, in a liquid suspension thegel structure produced by the interfacial forming technique (US. Patent2,708,617). The novel, non-rigid polymeric particle of this invention,hereinafter referred to as a fibrid, is capable of forming paper-likestructures on a paper-making machine. To be designated a fibrid, aparticle must possess (a) an ability to form a waterleaf having acouched wet tenacity of at least about 0.002 gram per denier when aplurality of the said particles is deposited from a liquid suspensionupon a screen, which waterleaf, when dried at a temperature below about50 C., has a dry tenacity at lea-st equal to its couched wet tenacityand (b) an ability, when a plurality of the said particles is depositedconcomitantly with staple fibers from a liquid suspension upon a screen,to bond a substantial weight of the said fibers by physical entwinementof the said particles with the said fibers to give a composite waterleafwith a wet tenacity of at least about 0.002 gram per denier. Inaddition, fibrid particles have a Canadian freeness number between 90and 790 and a high absorptive capacity for water, retaining at least 2.0grams of water per gram of particle under a compression load of about 39grams per square centimeter. By wholly synthetic polymeric is meant thatthe fibrid is formed of a polymeric material synthesized by man asdistinguished from a polymeric product of nature or derivative thereof.

Fibrid Pr0perzies.Any normally solid Wholly synthetic polymeric materialmay be employed in the production of fibrids. By normally solid is meantthat the material is non-fluid under normal room conditions. By anability to bond a substantial weight of (staple) fibers is meant that atleast 50% by weight of staple based on total staple and fibrids can bebonded from a concomitantly deposited mixture of staple and fibrids.

It is believed that the fibrid characteristics recited above are aresult of the combination of the morphology and non-rigid properties ofthe particle. The morphology is such that the particle is non-granularand has at least one dimension of minor magnitude relative to itslargest dimension, i.e., the fibrid particle is fiber-like or film-like.Usually, in any mass of fibrids, the individual fibrid particles are notidentical in shape and may include both fiber-like and film-likestructures. The nonrigid characteristic of the fibrid, which renders itextremely supple in liquid suspension and which permits the physicalentwinement described above, is presumably due to the presence of theminor dimension. Expressing this dimension in terms of denier, asdetermined in accordance with the fiber coarseness test described inTappi 41, lA-7A, No. 6 (June) 1958, fibrids have a denier no greaterthan about 15.

Complete dimensions and ranges of dimensions of such heterogeneous andodd-shaped structures are diflicult to express. Even screeningclassifications are not always completely satisfactory to definelimitations upon size since at times the individual particles becomeentangled with one another or wrap around the wire meshes of the screenand thereby fail to pass through the screen. Such behavior isencountered particularly in the case of fibrids made from soft (i.e.,initial modulus below 0.9) polymers. Hard polymers (i.e., initialmodulus above 0.9 g./denier) are more readily tested. As a general rulehowever, fibrid particles, when classified, according to the ClarkClassification Test (Tappi 33, 294-8, No. 6 (June) 1950) are retained tothe extent of not over 10% on a IO-mesh screen, and retained to theextent of at least on a ZOO-mesh screen.

Fibrid particles are usually frazzled, have a high specific surfacearea, and as indicated, a high absorptive capacity for water.

Preferred fibrids are those the waterleaves of which when dried for aperiod of twelve hours at a temperature below the stick temperature ofthe polymer from which they are made (i.e., the minimum temperature atwhich a sample of the polymer leaves a wet molten trail as it is strokedwith a moderate pressure across the smooth surface of a heated block)have a tenacity of at least about 0.005 gram per denier.

Identification of Figures.-The invention will be more readily understoodby reference to the figures.

Figures I and II illustrate typical technique embodiments suitable foruse in the process of the present invention. Each of the figures isdescribed in greater detail below.

Fibrid Production-The method for producing fibrids described and claimedin the present application consists in the beating of a liquidsuspension of the wet or gel structure produced by an interfacialforming process. In the interfacial forming process an interphasepolymerization is conducted between fast-reacting organic condensationpolymer-forming intermediates at an interface of controlled shapebetween two liquid phases, each of which contains an intermediate, toform a shaped condensation polymer. The process is described in UnitedStates Patent 2,708,617. One embodiment of the process is illustrated inFIGURE 1, In that figure reaction vessel 1 containing one of thefast-reacting organic condensation polymer-forming intermediates, 2, hasa complementary intermediate introduced from supply through 1 tube 3,the condensation polymer forming at the interface of controlled shape 4.The gel product 5 is withdrawn continuously from the interface overguides 6 and 7 in the form of a collapsed tube, the walls of which areno greater than about 0.020 inch in thickness, described and claimed inUnited States Patent 2,798,283 filed December 9, 1953. The tearing orshredding operation is accomplished by leading the tubular gel filament5, while still wet, into a vessel 3, containing liquid such as Water 9,which is being violently agitated by motor driven stirrer 10. A WaringBlendor is well adapted to perform this operation. The fibrids 11 form aslurry in liquid 9. In another embodiment of the process,

f; shown in FIGURE II, the thin film formed at the interface is shreddedto the fibrid form substantially as rapidly as it forms, simply bylocating stirrer 10 near interface 4 in vessel 1, which interface formsbetween polymerforming intermediates 2 and 12. This technique isillustrated in Example hereinafter. This process, described and claimedin the present application, is useful in preparing fibrids from anycondensation polymer, either linear or cross-linked, which can be formedby interfacial forming. The gel structure is destroyed on drying of theinterfacially formed structure and thereafter the structure will notform fibrids when beaten in liquid suspension as taught herein.

Test pr0cedures.The surface area of hard polymers is determined by atechnique based upon the adsorption of a unimolecular layer of a gasupon the surface of the sample while it is being maintained at atemperature close to the condensation temperature of the gas. Because ofthe excellent bonding properties of fibrids, the surface areameasurement is dependent to some extent upon the method of handling thesample prior to making the measurement. Accordingly, the followingstandardized procedure has been adopted. The first step is to wash thefibrids thoroughly with distilled water to remove all traces of residualsolvent. It is preferable to carry out the washing on a coarse sinteredglass funnel. During the washing a layer of liquid is maintained overthe fibrid mat at all times until the very last wash. The vacuum isdisconnected as soon as the water layer passes through the mat as thislast Wash is completed. The filter cake is then dried at 35 C. for atleast twelve hours followed by removal of the last traces of air andliquid by heating at 50 C. for at least one hour under vacuum until apressure as low as mm. has been reached.

The bulb containing the evacuated sample is immersed in liquid nitrogenand a measured amount of nitrogen gas is then brought into contact withthe sample. The amount adsorbed at each of a series of increasingpressures is determined. From these data the volume of adsorbed gascorresponding to the formation of a unimolecular layer of nitrogen onthe sample can be deduced, and from the known molecular area ofnitrogen, the specific area of the material is calculated. (See:Scientific and Industrial Glass Blowing and Laboratory Techniques, pp.257-283, by W. C. Barr and V. I. Anhorn, published by InstrumentsPublishing Company, Pittsburgh, Pennsylvania.)

Unless otherwise indicated, the strength of sheet materials preparedfrom hard polymers is determined by a modification of Tappi test T205m53wherein the pulp slurry is poured onto a 100-mesh screen to make a sheetwhich is washed with 10 liters of water, removed from the screen, anddried in an oven with air maintained at approximately 100 C. One-halfinch strips are cut from the sheet and strength measured on an Instrontester. The values are calculated on the basis of a one inch strip. Todetermine the wet strength one-half inch strips are cut from the driedsheet and placed in water, where they are soaked for 30 minutes at roomtemperature. The wet strength is also measured on an Instron tester andthe results calcuated on the basis of a one-inch Width.

The water absorption of hard polymers is measured by evenlydistributing, without compression, at two-gram sample of the testmaterial in a Buchner funnel (2 /2 inch diameter times 1 7 inch deep).One hundred ml. of water containing 0.1 gram of sodium lauryl sulfate ispoured over the sample and allowed to drain by gravity for about 1minute. The funnel is then connected to an overflowing reservoir so asto produce a /8 inch head of water in the funnel at equilibrium. Whenwater begins to flow into the funnel a No. 11 rubber stopper weighing67.4- grams is placed on the sample with the large face down. Atwo-pound weight is placed on the stopper. After ten minutes the petcockis turned to permit the sample to drain. After an additional ten minutesthe sample is removed and weighed.

Freeness is determined by Tappi test T227m50. The data obtained fromthis test are expressed as the familiar Canadian standard freenessnumbers, which represent the number of ml. of water which drain from theslurry under specified conditions.

Elmendorf tear strength is measured on the Elmendorf tear testeraccording to the procedure described in Tappi test T414m49. The strengthrecorded is the number of grams of force required to propagate a tearthe remaining distance across a 63 mm. strip in which a 20 mm. standardout has been made.

Tear factor is calculated by dividing the Elmendorf tear strength ingrams by the basis weight in g./m.

Tongue tear strength is determined in accordance with ASTM D-39.

Burst strength is measured on the Mullen burst tester according to theprocedure described in Tappi test T40m53.

Fold endurance is determined by Tappi test T423m50, using the MITFolding Endurance tester.

Elastic recovery is the percentage returned to original length withinone minute after the tension has been relaxed from a sample which hasbeen elongated 50% at the rate of 100% per minute and held at 50%elongation for one minute.

Stress decay is the per cent loss in stress in a yarn one minute afterit has been elongated to 50% at the rate of 100% per minute.

Initial modulus is determined by measuring the initial slope of thestress-strain curve.

The following examples are cited to illustrate the invention. They arenot intended to limit it in any manner.

Example 1 66 NYLON FIBRID BY BEATING INTERFACIAL STRUCTURE 25.15 ml. ofan aqueous solution containing 0.2138 grams of hexamethylenediamine perml. are mixed with 16.35 ml. of an aqueous solution containing 0.2155grams of sodium hydroxide per ml. and the combined solution diluted to100 ml. with water. This is carefully poured into a beaker containing100 ml. of a carbon tetrachloride solution in which 5.88 ml. of adipylchloride is dissolved, thereby forming two phases. A polymer film ofpolyhexamethylene adipamide) i.e. 66 nylon forms at the interface. Thisglm is drawn out continuously over a wet feed roller at a rate of about18 ft./min. into a Waring Blender in which about 200 ml. of ethylalcohol containing 3 ml. of hydrochloric acid is being stirred rapidly.After the process is continued for 2.5 minutes the product in the WaringBlender is collected on a Buchner funnel with a sintered glass bottomand washed well with aqueous alcohol and water.

Two such preparations, combined in 3 liters of water, are poured on an8" x 8 l00-mesh screen in a hand sheet box, vacuum being applied as soonas the fibrids are properly suspended in the liquid in the hand sheetbox. After all of the water has been removed, the sheet is blotted onceon the screen. It is then removed from the screen, placed betweenblotters, and rolled with a steel rolling pin. After the sheet is driedon a paper dryer at C. for approximately 10 minutes, it has a drytenacity of 0.364 grams/denier at a dry elongation of 46% and a wettenacity of 0.094 gram/denier at a wet elongation of 33%.

A slurry of the fibrids from which the sheets are made are observed tohave a Canadian Standard freeness of 120. The surface area is 8.3 mfi/g.A ratio of wet to dry weight of 11.9 is noted when the weight of a sheetformed on a Buchner funnel with the water just drawn out is comparedwith the weight of the same sheet dried to constant weight at roomtemperature.

Example 2 ea NYLON FIBRID BY BEATING INTERFACIAL STRUCTURE The processof Example 1 is modified by collecting the withdrawn film in an 800 ml.beaker containing a solution of 392 ml. of ethyl alcohol and 8 ml. ofconcentrated hydrochloric acid. After 10 minutes the film is choppedinto len ths approximately one inch long which are added to the WaringBlendor containing the solution as described in Example 1, the saidblendor being operated at full speed. After 2 minutes the fibrids formedare filtered ofi on a fritted glass Buchner funnel.

A 1.8 gram sample of the above is washed well and suspended inapproximately 3 liters of water and a sheet formed in a hand sheet boxand thereafter finished as described in Example 1. The sheet has a drytenacity of 0.255 gram/ denier at a dry elongation of 27% and a wettenacity of 0.059 gram/denier at a wet elongation of 18%. The ratio ofwet to dry weight is 15.

The fibrids have a surface area of approximately 7.3 m. /g. An aqueoussuspension of these fibrids has a Canadian Standard freeness of 154.

Example 3 610 POLYAMIDE FIBRID BY BEATING INTERFACIAL STRUCTURE Thetechnique of Example 1 is followed, using a solution of 8 ml. of sebacylchloride (10 acid) in 632 ml. of carbon tetrachloride as one phase and,as a second phase, a solution formed by mixing 21.62 ml. of an aqueoushexarnethylenediarnine (6 amine) solution containing 0.202 gram ofdiamine per ml. with 15.34 ml. of an aqueous sodium hydroxide solutioncontaining 0.196 gram of sodium hydroxide per ml., and diluting to atotal volume of 94 ml. with water. The film, 610 polymer, which isformed at the interface is fed at the rate of 20 ft./min. for minutesdirectly into the Waring Blender containing a 50/50 mixture of ethylalcohol and water containing by weight of hydrochloric acid. When anaqueous suspension of the product is dewatered on a Buchner funnel acohesive structure is formed.

Example 4 66 NYLON FIBRID BY BEATING INTERFACIAL STRUCTURE Example 1 ismodified to pass the film as a ropelike mass over a bobbin at 12ft./min. into the Waring Blendor operating at about 80% of full speed.Several five gram batches of fibrids having the appearance of narrow,twisted, irregular ribbons are prepared by this procedure. Thissuspension has a Canadian Standard freeness of U3. A 3 gram, 8 inchsquare hand sheet prepared from these fibrids has a dry tenacity of 7.93lbs./in./oz./yd. and a maximum tongue tear of 0.187 lb./in./yd.

A hand sheet of the same size and weight is prepared from a mixturecontaining 50% by weight of the fibrids prepared as described above and50% by weight of 3/ 8 inch, 2 d.p.f. 66 nylon [poly(hexamethyleneadipamide)] staple. This sheet has a dry tenacity of 4.62lbs./in./oz./yd. and a maximum tongue tear of 0.557 1b./oz./yd.

The sheet of fibrids and nylon staple is heated to a temperature of 200C. while being pressed at about 1000 lbs./in. A high strength (13lbs./in./oz./yd. sheet material having a relatively smooth surfaceresults. The fibrids appear to have fused uniformly throughout the sheetproduct.

As exemplified above the interfacial spinning technique produces astructure which can be shredded to form fibrids. Interfacial spinningbroadly considered involves bringing a liquid phase comprising onecondensation polymer-forming intermediate (e.g., a liquid organicdiarnine or solution of an organic diamine) and another liquid phasecomprising a coreacting polymer-forming 6 intermediate (e.g., a solutionof an organic dicarboxylic acid halide) together to form a liquid-liquidinterface, controlling the shape of the interface until a shaped polymerhas formed, and then withdrawing the polymer from the interface.Preferably, the polymer is withdrawn continuously from the interface asa continuous self-supporting film or filament. Tearing or shredding ispreferably performed upon the freshly-made shaped structure. This isconveniently done by leading the film or fiber directly into a suitableshredder, as shown in Examples 1 and 3. Alternatively the interfaciallyspun structure may be collected and stored in the wet state between thespinning and shredding operation, as shown in Example 2. Anothersuitable procedure is to withdraw the film formed at the interface inconsecutive batches, which are then shredded or beaten, rather than toremove the interfacially-formed structure continuously. When operatingin this manner the interfacially-formed film may be gently agitated toincrease its thickness and thereafter shredded in a liquid suspension.In another modification of this process, the thin film formed at theinterface is shredded to the fibrid form substantially as rapidly as itforms. Agitation is controlled to avoid dispersing onereactantcontaining phase in the other prior to formation of theinterfacial film. Suitable conditions are described in EX- ample 5below.

Example 5 66 NYLON FIBRID BY BEATING INTERFACIAL STRUCTURE 200 ml. of anaqueous solution containing 9.27 grams hexarnethylene diamine and 6.4grams sodium hydroxide are placed in a Waring Blendor jar. The blendoris started at half speed to permit formation of an interfacial film and11.76 ml. of adipyl chloride dissolved in 400 ml. of carbontetrachloride is added through a powder funnel inserted in the cover.The addition is made rapidly and the mass of forming polymer stops thestirrer almost immediately. The blades are freed of the product with aspatula and stirring of the mass is continued for 3 minutes producingthe fibrid product.

The product is isolated and washed thoroughly with alcohol and water.The particles are of a twisted, ragged and branched filmy structure.Strong sheets are prepared by drawing down the dispersion of particleson a sintered glass funnel and drying the mat. The inherent viscosity ofthe polymer is 0.80 (m-cresol at 30 C. and 0.5 gram polymer/ ml.solution).

It is necessary, both to facilitate shredding and to obtain highstrength in sheet products, that the interfacially-spun structure be ina highly-swollen condition when it is shredded. This is accomplished bybeating without intermediate drying.

The interfacially-formed structure is shredded while suspended in anon-solvent liquid. Suitable shredding or shearing media include water,glycerol, ethylene glycol, acetone, ether, alcohol, etc. A choice ofliquid is dependent upon the nature of the interfacially-formedstructure. Aqueous organic liquid mixtures, such as waterglycerol orwater-ethylene glycol mixtures, are useful in the process. Water aloneis particularly desirable for economic reasons and works quitesatisfactorily in many cases. Non-aqueous media are sometimes desirable,however, particularly to retard crystallization of the polymer as it isshaped. A relatively wide range of viscosities may be tolerated in theshearing medium.

Shredding of the interfacially-formed structures suspended in the liquidis conveniently performed by turbulent agitation. The design of thestirrer blade used in the "Waring Blender has been found to beparticularly satisfactory. Shredding action can be increased byintroducing suitable baflles in the mixing vessel, for instance, as usedin the commercial mixing devices of the Waring Blendor type. Other typesof apparatus, such as disc mills, Jordan refiners, and the like, aresuitable.

speasar For a device to be suitable for use in this process, it isnecessary that it be capable of tearing or shredding the gel structurein the liquid medium to produce fibrous structures with a minimum sufacearea of above about 4.5 m. g. The mechanical action required to producethis is, of course, dependent to some extent upon the gel swellingfactor and the physical form of the polymer mass to which the shear isapplied.

The shredding process forms a slurry of heterogeneous fibrids. TheCanadian Standard freeness numbers of aqueous slurries of the fibridsobtained by shredding are below about 750 and the preferred products ofthis invention have freeness numbers in the range between about 150 and500. The freeness and many other characteristics of these slurries aresimilar to those of cellulose pulps used for making paper. They are,therefore, of particular utility in the manufacture of sheet-likeproducts on paper-making equipment. As shown in the examples above,these sheet-like structures can be made from the fibrids alone or may beformed from a mixture of fibrids and staple. The fibrids bond togetherto form coherent sheets when settled from liquid suspension, forinstance, on a screen. Where mixtures of staple and fibrids aredeposited, their wet sheets can be handled. When such sheets, afterdrying, are subjected to heat and pressure the fibrids may be fused, asshown in Example 4. In this way a very strong and uniform sheet can beproduced.

Fibrid Slzeets.As shown in the previous examples an importantcharacteristic of fibrids is their cohesiveness or bonding strength insheet products. This is quite evident in both wet and dry sheets,particularly when the sheets are compared with the products of the priorart. For example, the wet tenacity of sheets prepared from staple fibersis usually less than 4 10 gram/denier. In contrast to this, sheetsprepared from hard polymer fibrids have a minimum couched wet tenacityof about 0.002 gram/denier, and frequently have minimum dry strength,before pressing, of about 0.01 gram/denier. A Wet strength of as high as0.02 gram/denier is not imusual for these products. The values expressedin grams/denier may be converted to values expressed as lbs./in./oz./yd.by multiplying by 17.

Plyn'1ers.--Suitable polymers include polyamides, such aspoly(hexamethylene adipamide), poly(ethylene sebacantide),poly(methylene bis (polycyclohexylene) adipamide), polycaprolactam, andcopolyamides, such as those formed from a mixture ofhexamethylenediamine, adipic acid, and sebacic acid, or by a mixture ofcaprolactam, hexamethylenediamine, and adipic acid; polyurethanes;polyureas, polyesters, such as poly(ethylene terepht'nalate);polythiolesters; polysulfonamides; and many others. Copolymers of alltypes may be used. Derivatives of the polymers are also suitable.

Many types of condensation elastomers are also suitable. United StatesPatent No. 2,670,267 describes N- a kyl-substituted copolyamides whichare highly elastic and have a suitable low modulus. A copolyamide ofthis type, obtained by reacting adipic acid With a mixture ofhexamethylenediamine, N-isobutylhexamethylenediamine, andN.N-isobutylhexamethylenediamine produces an elastomer which isparticularly satisfactory for the purposes of this invention.

Free/less Numbers. The freeness numbers of aqueous slurries of fibridsis below about 790. The preferred fibrids from hard polymers havefreeness numbers in the range between about 100 and about 600. The preferred products from soft polymers have freeness in the range betweenabout 4-00 and about 700.

The freeness and many other characteristics of fibrid slurries aresimilar to those of cellulose pulps used for making paper. The primarydistinction is that the slurries are prepared from synthetic polymers.Accordingly, they may be thought of as synthetic pulps. Thepropercjltulose derivatives, and/or by mixing with beaten celluwseand/or natural animal fibers and/ or mineral fibers. Many other methodsof modifying these slurries are mentioned elsewhere.

isolation of Fibria's.-lf it is desired, the fibrids prepared from hardpolymers may be isolated and dried. The drying conditions required forretention of adequate bonding properties in sheet formation on apapermaking machine are not particularly critical, although it ispreferable that these conditions not be drastic. For example, thetemperature should be kept low enough to avoid fusing the fibrids intoglobular masses, since the bonding roperties associated with theseproducts would be lost. Also, severe mechanical action should beavoided, since this would tend to break up the fibrids into fines. Morecare in drying fibrids is required if it is desired that they havebonding properties when redispersed in water identical with those whichthey possessed prior to drying.

One method of drying which has been found suitable for preparing driedfibrids with adequate bonding properties is to spray-dry a slurry undercontrolled conditions, e.g., the temperature should not be too close tothe melting point and the slurry which is sprayed should besubstantially free of solvent for the polymer. A second method is towash the fibrids with a water-miscible lowboiling organic solvent. Thewater-miscibility requirement is based on the assumption that thefibrids have been deposited from an aqueous slurry and are still wet.

Another suitable method comprises removing water in a centrifuge untilthe moisture content has been reduced to approximately The fibrids arethen placed in a cone with an air inlet at the apex. Air is admitted atapproximately 9 cu. ft./ min. to circulate the fibrids. Afterapproximately three minutes the moisture content is reduced to about50%. The fluffed fibrids are then transferred to an air oven where themoisture content is reduced to approximately 1% by circulating heatedair; temperatures in the region of 100 C. are usually suitable.

Redispersion of Fibrids.The dried fibrids prepared from hard polymerscan be redispersed in aqueous media, from which can be made sheetproducts with substantially the same properties possessed by sheetsprepared directly from the original slurry. Redispersing is usuallycarried out in an apparatus such as the Hollander heater and is aided bythe use of wetting agents. The processing economies of preparing thesheet products from the original aqueous slurry are obvious, and this isnaturally the preferred method of operation wherever feasible. However,since it may frequently be necessary to ship the fibrids from thelocation where they are prepared to another location, where they will beconverted to sheet products, it is a definite advantage to be able todry the products to reduce shipping costs.

Fibrid Sheets.An important characteristic of fibrids is theircohesiveness or bonding strength in sheet products. This is quiteevident in both wet and dry homosheets. Sheets prepared from softpolymer fibrids have a minimum couched wet strength of approximately0.002 g.p.d. and a minimum dry strength, before pressing, ofapproximately 0.005 g.p.d. This exists despite a low level of mechanicalproperties characteristic of the polymers per se, when compared to hardpolymers. One characteristic of these sheets, which distinguishes themfrom homosheet products prepared from hard polymer fibrids is theirbehavior on rewetting after drying. The sheets from soft polymer fibridsretain a substantial percentage of the dry strength whereas theupressed, unfused homosheets prepared from hard polymer fibrids dropback more nearly to a strength level of the original wet sheet, a valuewhich is frequently appreciably lower than the dry strength. The wettenacity of sheets prepared from staple fibers is usually less than4X10" gram/denier. Sheets prepared from hard polymer fibrids have aminimum couched wet tenacity of about 0.002 gram/denier and a minimumdry strength before pressing of about 0.005 gram/denier. A wet strengthof as high as 0.02 gram/ denier is not unusual for these products.Values expressed as gr-am/ denier may be converted to values expressedas lbs./in./oz./yd. by multiplying by 17.

By virtue of their special characteristics, fibrids disperse readily toform stable dispersions which may be used in ordinary papermakingoperations without adding surfactants. This permits the use of fibridsin papermaking machinery without modification of the usual processingconditions, and serves to distinguish fibrids from any previously knownfiber form of synthetic polymer. Thus, fibrids may be added to thebeater and passed through the refiner into the head box onto the screenof a Four-drinier machine. From there the sheet may be carried to thewet press through drier rolls, caienders, and woundup as a sheet withoutmodifying the normal operating characteristics of the machines as usedfor making cellulose paper. In addition, the papermaking operation canbe integrated with fibrid manufacture by collecting the fibrid on ascreen at the exit from the precipitation zone. It is also possible toform shaped article directly from thick fibrid slurries by slush-moldingin patterns or molds.

The advantages of these fibrids in the formation of sheet productsbecomes more apparent when sheet products from hard polymers arecompared to those from synthetic polymers in the fiber forms prepared byprior art processes.

Table XVI Wet Sheet 2 Fiber form Surface area 1 Freencss strengthunnress.

unlused fibers Hard Polymer above 2.0 below 790. above 0.002.

Fibrids. Microfibers approximately above 800. Aqueous slurries 1.0. andsheets very ditficult to form.

Air Jetted Fibers 0.5.. Do. Fibers From Fibril- 1.1.-.. 4X10.

latable Films. Staple less than 0.5--- do N greater than 1 MJ/g. 2 Gr)(1. 3 Fine, round, dense fibers with a diameter of approximately twomicrons or less.

4 Equivalent to those described in U.S. 2,483,405.

An important feature of the bonding properties of fibrids is that noheat or pressure is required to develop adequate strength. The geometryof the sheet is determined primarily by the fcrm in which it is heldwhile being dried at room temperature. The strength of sheet productscomprising soft polymer fibrids can be increased by heating alone. Thisis also true to a lesser extent for products comprising hard polymerfibrids, but for these products maximum strength is usually attained bythe combination of heat and pressure.

Pressure rolls and solvent treatments, applied as known in the art,generally tend to produce stiffer, less porous sheets. Engraved rollscan be used to produce patterns on these sheets, for example, by formingtranslucent areas in an opaque background. Another way of introducing atexture or pattern on the sheet is to pass it through a calender whichhas one roll surfaced with heated fine needles or spikes. Such atreatment may also serve to increase the bonding.

Fibrid-Bonded Products-When using fibrids as a binder in sheetformation, as little as about 1% fibrids in the final sheet is oftenhighly advantageous. Generally, however, it is preferred to use at leastabout 5% of the fibrid and at least about 15% fibrid is preferred formaximum strength.

The hand and other properties of sheet products prepared from hard and/or soft fibrids can be controlled and 10 modified in many ways. One verypractical method of accomplishing this is to blend the fibrids of thisinvention with staple fibers. These staple fibers may be derived fromcellulosic materials, staple of synthetic polymers, or staple fibers ofnatural origin. The combination of fibrids with staple generally resultsin a sheet with higher tear strength. Within this area the propertiescan be controlled or modified by the choice of polymer for preparing thefibrids, the choice of staple fiber composition and/ or length and/ ordenier.

The properties of fibrid-bonded sheets, whether they be homosheets(i.e., all fibrid) or heterosheets, i.e., sheets from mixtures of fibersand staple, may be controlled or modified by calendering or heating. Forexample, fibrid homosheets may be made paper-like by calendering alone.A wide variety of products may be made by the use of a combination ofheat and pressure. The properties obtained are controlled by the amountand type (dead load or calender) of pressure applied, calenderingtemperature, and the like.

Urility.-Products bonded with fibrids have many applications. One ofthese is in the form of elastic apparel. Such applications includeouterwear garments such as jackets, coats, skirts, playsuits, underwater suits, rainwear, gloves, watch straps, and in certain shoeapplications, such as in house slippers, foot-wear-uppers, and boot andshoe liners. Other apparel and personal items include girdles, elasticfabrics for anklets, wristlets, waist bands, and sweatbands, handbags,sleeping bags, and elastic medical materials, such as surgical andmedical bandages. Household uses include antiskid mats, such as ruganchors and tub mats, blankets, shower curtains, and protective coversfor such items as coasters, bottles, drinking glasses, luggage, lampshades, and the bases of lamps, statues, and silver. Furtherapplications are in Wall covering, draperies, and in coated fabrics.They may be used in the manufacture of books, such as in book binding orcovering whether it be the only cover or as a protective cover forhard-bound books. In connection with applications such as this, it isinteresting to note that sheet products made from certain of theelastomer fibrids are heat-scalable. Use as flannel replacements, suchas in apparel, pool table covers, and phonographic turn table covers issuggested by the properties of the sheet products. They may be used aslinings or inserts, such as fabric interliners, linings for a variety ofcases such as those used for scientific instruments, jewelry, musicalinstruments, etc.

Sheet products prepared from hard polymer fibrids, or combinations ofthese fibrids with hard polymer staple, have properties which suggestmany possible uses. Thus, the 'ood dimensional stability, excellentresistance to acids and alkalies, relatively low water absorption, goodWet strength properties, and resistance to attack by fungus and moldsuggest their use in non-woven products utilized in such applications aslight weight tarpaulins and tentage material. Other applications outsidethe usual paper and tape uses are as paper drapes and curtains, basesfor coated fabrics, abrasive backings, diaphrgm reinforcements, bookcovers, both as the sole backing or as covers for other types of bookbindings.

ing stored.

An important application for paper-like products is in the field ofbagging, particularly for heavy industrial uses. However, additionalspecific uses are as vacuum cleaner bags, shoot bags for pollenationcontrol, sleeping bags, and tea bags.

Other industrial applications include electrical insulation, transformerpress boards, and as wrappings for underground pipes. They may also beused as wrappings for food products, such as meat and cheese. Additionalapplications include filter media, such as filter papers, fuel cells andmold release materials.

As an example of a variety of protective cover applications may bementioned covers for military equipment which is be-- Sheet productscomprising these fibrids are also ideally suited for use as headlinersin automobiles, interliners for non-woven fabrics, and reinforcingagents for rubber goods, such as belting and tires. Fabric-like sheetsof a cashmere or suede type are formed by brushing a nap on a sheetcontaining fibrids from either hard or soft polyme Many equivalentmodifications will be .apparent to those skilled in the art from areading of the above without a departure from the inventive concept.

This application is a division of United States applica tion 788,371,filed January 22, 1959, now Patent No. 2,999,788.

What is claimed is:

l. A process for the production of a fibrid slurry which comprises thesteps of forming a shaped gel structure of an organic condensationpolymer by an interphase polymerization between fast-reacting organiccondensation polymer-forming intermediates at an interface of controiledshape between two liquid phases, each of which contains intermediate andbeating a liquid suspension of the shaped structure so formed prior todrying the said shaped structure.

2. The process or claim wherein the interfacially spun product in theform of a collapsed tube is continuously led from its interfacialspinning device to a shredding liquid.

3. The process of claim 2 wherein the said shredding liquid is water.

4-. The process of claim 1 wherein the said interfacially formedstructure is a polyamide.

5. The process of claim 4 wherein the said polyamide 5-;polyl'lexamethylene adiparnide.

6. The process of claim 4 wherein the said polyarnide ispolyhexainethylene sebacarnide.

Vtooding Oct. 22,

Rasmussen Oct. 4,

FOl2. "-N PATENTS Great Britain Apr. 20,

1. A PROCESS FOR THE PRODUCTION OF A FIBRID SLURRY WHICH COMPRISES THESTEPS OF FORMING A SHAPED GEL STRUCTURE OF AN ORGANIC CONDENSATIONPOLYMER BY AN INTERPHASE POLYMERIZATION BETWEEN FAST-REACTING ORGANICCONDENSATION POLYMER-FORMING INTERMEDIATES AT AN INTERFACE OF CONTROLLEDSHAPE BETWEEN TWO LIQUID PHASES, EACH OF WHICH CONTAINS AN INTERMEDIATEAND BEATING A LIQUID SUSOENSION OF THE SHAPED STRUCTURE SO FORMED PRIORTO DRYING THE SAID SHAPED STRUCTURE.